1. Technological Field
This technical disclosure pertains generally to tunable notch filtering within an RF front-end, and more particularly to tunable filters utilizing distributedly modulated capacitor (DMC) technology.
2. Background Discussion
In wireless communication systems it is important to separate the receiver input signal from interferences from the air, receiver output, or from a transmitter. Providing this RF frequency separation requires a sharp filter in the front-end of the communication circuit (receiver or transceiver), which often takes the form of diplexer or multiplexer. Using a tunable filter minimizes the noise and distortion caused by those interferences and is essential for receptions with both high sensitivity and high dynamic range. Yet, it is limiting to have the front end constrained to a particular fixed frequency of operation.
Tunable MEMS cavity filters are an example of current state of the art tunable filters. These filters, however, require a large volume and high tuning voltages up to about 100 volts, while they suffer from very large insertion losses.
Accordingly, a need exists for tunable DMC filters which are suitable for miniature circuitry while exhibiting low insertion losses. The presented tunable filters overcome the shortcomings of prior filters, while providing additional benefits.